The invention relates to a novel vault for industrial furnaces, such as glass and metallurgical furnaces.
Numerous industrial furnaces, such as those used in glass-making and metallurgy, have vaults or crowns comprised of a plurality of arches made of archstones or keys, the extreme archstones of which abut on skew blocks which rest generally on the side walls of the furnace through the intermediary of expansion joints. The archstones of the vault are subjected to very heavy thermal radiation and must be sufficiently refractory to withstand the temperature to which they are raised as well as the action, at this temperature, of the corrosive agents present in the atmosphere of the furnace.
The vaults, which are usually used at the present time in glass furnaces, are comprised of archstones of agglomerated silica of relatively large thickness with a thermal insulation above the archstones. Only a limited thermal insulation is possible when using such archstones because the mechanical strength of agglomerated silica decreases very rapidly at high temperature. Consequently, one is obliged to accept an important loss of heat from the vault towards the exterior and to use archstones of relatively large thickness, so that the temperature of the archstones in the zone next to their top face remains compatible with the retention of a sufficient mechanical strength. Assuming that the temperature of the bottom face of the vault is of the order of 1500.degree.C, the thermal insulation is adjusted so that the temperature of the top face of the vault does not exceed 1100.degree.C. Obviously, the economy of furnaces provided with such vaults is poor due to the important loss of heat. Further, the corrosion resistance of agglomerated silica is also poor so that it is necessary to change the archstones of the vault after a relatively short period of service, for instance every one or two years, which make it necessary to stop the operation of the furnace.
It has been also suggested in U.S. Pat. No. 2,277,507 to construct suspended arches in furnaces by using fused cast refractory blocks having a large central cavity filled with granules of heat-insulating material united to one another and to the walls of the cavity. However, the construction of suspended arches implies the use of suspending elements, usually in metal, the mechanical strength of which is poor at elevated temperatures so that it is not possible, with such a construction, to have a highly efficient thermally insulating structure above the disclosed blocks so that the economy of the furnaces equipped with vaults made of such suspended arches would remain poor. Further, the manufacture of the disclosed blocks is poorly feasible at an industrial scale and, to the knowledge of the applicants, such suspended arches have not received industrial success.